Hydraulic valving device



April 18, 1961 H. THOMAS HYDRAULIC VALVING DEVICE 5 Sheets-Sheet 1 Filed Sept. 6, 1956 April 18, 1961 5 Sheets-Sheet, 2

Filed Sept. 6, 1956 INVENTORZ HEINRICH THOMAS ATTORNEYS.

April 18, 1961 H. THOMAS 2,980,072

HYDRAULIC VALVING DEVICE Filed Sept. 6, 1956 5 Sheets-Sheet 3 April 18, 1961 Filed Sept. 6, 1956 'H. THOMAS 2,980,072

HYDRAULIC VALVING DEVICE 5 Sheets-Sheet 4 vwawm April'l8, 1961 H. THOMAS HYDRAULIC VALVING DEVICE 5 Sheets-Sheet 5 Filed Sept. 6, 1956 lowesfpressure P;

5 f f 0 J0 .35 5 arm R m5 0 m H w R M fl 2,980,072 Patented Apr. 18, 1961 ice HYDRAULIC VALVING DEVICE Heinrich Thomas, 91 Altenaer Strasse, Hemer-Westig,

Germany Filed Sept. 6, 1956, Ser. No. 608,301

Claims priority, application Germany Sept. 6, 1955 9 Claims. (Cl. 121-464) The present invention relates to a valving system and more particularly, to a pilot valve arrangement for controlling the action of pistons of hydraulically powered machines.

There have been employed heretofore for the control of machines provided with hydraulically operated pistons sliding controls which require, even when provided with an extremely fine finish, large sealing surfaces for the stufling of the slide outlets. The result is large slide ways and large slide masses and a considerable reduction of the number of strokes, so that conventional controls of this kind are usually inefficient with respect to the number of cycles per unit of time. This is true even in cases where, in order to avoid large slide masses, high pres sure oil is employed, as these high speeds result, through turbulent currents and frictional losses in the oil channels, in considerable heating of the oil, which in its turn limits the number of cycles.

The object of this invention is to employ for reciprocatign pistons of various kinds of machines operated with hydraulic fluid a control which provides a laminar oil flow, and in this way prevents overheating, and which works practically without inertia in order to increase in this way the number of the impulse cycles as much as possible.

In conformity with this object of the invention, the invention is characterized by the use of a pilot valve consisting of an inlet valve, an outlet valve, and a valve pin or valve slide guided in the valve bodies and controlled from without, and by whose longitudinal movement in one direction a control chamber positioned between the two valves to be displaced with respect to each other is acted on by the pressure of the oil to be fed to it for the opening of the inlet valve, while simultaneously pressure oil is fed via the opened inlet valve to the working cylinder of the machine for the movement of the working piston, and by whose longitudinal movement in the other direction, for the purpose of achieving the return movement of the piston, this control chamber is brought into communication with a flowofi chamber for the closing of the inlet valve and for the opening of the outlet valve.

The valve system of the present invention opens with relatively small movements relatively large pathways of flow for the passage of hydraulic fluid from the pump, so that a laminar flow of hydraulic fluid is achieved without heating. The regulating forces active at the valves are very large as compared with their mass, whereby also the movements, effected from without, of the valve pin or valve slide, whose mass is very small and for that reason permits a high number of cycles, are insignificant as compared with the valves, so that the control works practically without inertia. The novel pilot valve makes a superfinish for sealing surfaces unnecessary, as the valve heads can easily be produced with the necessary finish without special machinery, because leakage from the control chamber is of no concern, as any leakage will always be directed in the direction of the oil flow, as will be seen from the forms of construction hereinafter described. The required actuating force (forces) needed for the reversed operation of the valves, which may be of the electrical, hydraulic or mechanical kind, is relatively small, and the means for producing the valve actuating force is of relatively small dimensions.

The novel pilot valve may be employed for any kind of hydraulic machine which includes reciprocating pistons, such as bending machines, hydraulic presses, copying controls and the like, and is suited for the open and closed regulation, as well as for the stepless variable, sensitive opening and closing.

Additional features and advantages of the invention will be understood from a consideration of the following detailed description taken in connection with the accompanying drawings, forming a part of this specification and in which two embodiments of the invention have been shown by way of example. However, it is to be understood that the invention is not confined to any strict conformity with the showing of the drawings but may be changed or modified, so long as such changes or modifications mark no material departure from the salient features of the invention as expressed in the appending claims.

In the drawings:

Fig. 1 is a longitudinal sectional view of the operating unit of a bending machine and of the means for actuating the pilot valve;

Fig. 1a is an enlarged sectional view of the pilot valve of Fig. 1;

Fig. 2 is a sectional view diagrammatically showing a hydraulic press provided with modified pilot valves of the invention;

Fig. 3 is a sectional view, on an enlarged scale, of the pilot valves of Fig. 2;

Fig. 4 shows a pressure diagram for the operation of the valves.

The embodiment shown in Fig. l is an example of an operating unit of a hydraulically actuated bending machine, whereby, for example, up to twelve of such operating units are mounted on a supporting base in a desired or required angular position with respect to one another.

The operating unit consists of a piston a devised as a differential piston and composed, for example, of two parts secured to each other by means of screws 1, and of a cyiinder b. The piston a is at its outer end provided with mounting or clamping devices for bending tools. The piston a moves, with a portion a of enlarged diameter offiset at 2 and 3, in the cylinder chamber 4 and is additionally guided at the ends of the cylinder. Special packing rings or the like may be provided here.

As is apparent in the drawings, the piston 11' forms the casing of the novel pilot valve. The hydraulic fluid, supplied by a pump, is fed via a longitudinally extending channel 5 (indicated in Fig. 1 through hatching) of the cylinder b and via a plurality of radially extending bores 6 to an inlet valve chamber 7. This valve chamber 7 is closed up by a valve head 8 ofan inner valve body 9. When the valve 3 is open, the inlet valve chamber 7 is via a plurality of longitudinal bores 10 of the piston a in communication with the cylinder chamber 4, and with an outlet valve chamber 11. The outlet valve chamber 11 is closed up by a cylindrical hollow outlet valve 12, resting tightly against a seat of the piston a, or is, when the outlet valve 12 is open, via the hollow piston end 0 in communication with chamber 13 of the cylinder b, in which the oil is maintained at 14 by a store vessel (not illustrated in the drawings) and by a spring loaded valve at a slight overpressure of, for example, 2.5 atm.

The cylindrical inlet valve body 9 is provided between the inletand outlet valve heads 8 and 12 with an offset portion 9a of enlarged diameter, whose offset shoulder facing the inlet cooperates with a stop ring 15 of the piston a for the limitation of the opening movement of the inlet valve 8, 9, and whose opposite offset shoulder and the confronting face of the outlet valve 12 close up the control chamber 16 which is bordered by the inner piston surface and by the circumference of the end 91) of the inlet valve body 9 on which the outlet valve 12 is guided.

The inlet valve body 9 is provided with an axial bore in which is located a valve pin c consisting of a guide piston 17, a pin-shaft 18, and a valve head 19 bearing on the outlet side against the end of the axial valve body bore.

The inlet valve chamber 7 is, by means of radial bore 20, radial bore 90, passageway 21, and radial bores 22 and 22a, in constant communication with the control chamber 16, and with the annular chamber 23 surrounding the valve pin shaft 18. The bore within inlet valve body 9 is of narrow diameter to such an extent that the flow of hydraulic fluid from the inlet valve chamber 7 into the control chamber 16 is thro ttled.

For the actuation of the pilot valve, for the reciproca- L'on of the operation piston, actuating means are required, which may operate either electrically, mechanically or hydraulically, and by means of which is maintained a predetermined relative position of the inlet valve with respect to its valve seat and of the valve pin head with respect to its seat, that is to say, a closed position of the inlet valve and an open position of the valve pin head during the return movement, and an open position or closed position of these two valves during the forward movement of the working piston, while the movement of the outlet valve automatically controls itself. A hydraulically operated valve actuating means will hereinafter be described.

The inlet valve 8, 9 is closed by the pressure of the hydraulic fluid upon the annular surface determined by the valve seat diameter and the diameter of the inlet valve body 9. The spring 24 increases this closing force for reasons which will be explained later. The opening of the inlet valve is effected by the pressure existing in the control chamber 16, which pressure acts upon the annular surface formed by the outer diameters of the inlet valve body 9a and 9b. The outlet valve 12 opens because of the pressure existing behind the offset end 3 of the piston a, which pressure acts against the annular surface formed by the valve seat diameter and outer diameter of the outlet valve 12. This opening force is increased by the action of the spring 25. The closing of the outlet valve 12 is effected by the pressure in the control chamber 16, which pressure acts upon the annular surface formed by the diameter of the valve body end 9b and the outer diameter of the outlet valve 12. A slight effect is produced also by the inner annular surfaces of the pilot valve, which inner annular surfaces are acted on by the outflow pressure existing in the chamber 13. The four surfaces of the pilot valve acted on by the pressure are so differentiated with respect to one another that increase of pressure in the control chamber 16 first closes the outlet valve 12, and that further increase of pressure results in an opening of the inlet valve 8, 9, while, on the other hand, decrease of pressure in the control chamber 16 renders an opening of the outlet valve 12 possible only after the inlet valve 8, 9 has completely closed.

In Fig. l, a working stroke has just been completed. The inlet valve 8 is closed at this moment, whereby the valve pin head 19 is lifted by the pilot valve actuating means off its seat, because of the communication of the control pressure in the control chamber 16 with the flowoff chamber 13, the control pressure dropping to the pressure in chamber 13, so that in the control chamber 16 there are no longer forces active which would force the two valves apart. The hydraulic fluid flowing into the cylinder b can, when the inlet valve is closed, act only upon the annular surface 2 of the working piston. This pressure causes in the cylinder chamber, behind the annular surface 3, a counterpressure, which opens with the aid of the spring 25 the outlet valve and which maintains the flow-off of the oil from this chamber via the outlet valve, the hollow extension a of the piston, and the flowoif chamber 13. As in the flow-off chamber a counterpressure exists, the return movement of the piston is thereby cushioned.

During the return movement of the working piston, the valve pin c, maintained by the spring 42 in position for opening of the valve head 19, is carried along. If this valve pin is arrested by the preliminary control means to be described later, the valve head 19 closes the control oil outlet, so that the operating pressure prevailing in the inlet valve chamber 7 immediately affects the control chamber 16. The pressure of the control chamber is increased and the outlet valve closes, whereby the return movement of the working piston is brought to an end. If, at high speed of the working piston, this end position is traversed, the pressure in the control chamber 16 rises up to the operating pressure, with the result that the inlet valve 8, 9 opens and that the working piston moves forward a very slight distance. For, the forward movement of the working piston has the immediate result that the valve pin head 19 is again lifted off its seat and that through reduction of the control chamber pressure the inlet valve 8, 9 is closed. When the control pin 0 is arrested, the working piston adjusts itself automatically to such position that the control oil flow-oif at the valve head 19 corresponds exactly to the control oil supply through the throttle bore 20. Through suitable differentiation of the four surfaces of the pilot valve acted on by pressure (as mentioned in the preceding paragraph) and by changes in throttle bore 20, whose diameter aifects the quantity of the control oil, the pilot valve can be devised for retarded or very quick action.

As soon as, by means of the preliminary control means, the control pin 0 is pressed, the pressure within the control chamber 16 rises, as hereinbefore already described. As a result of this, the inlet valve 8, 9 opens, the pressure oil flows into the space behind the offset surface 3 of the working piston and displaces the latter in forward direction. The opening movement of the inlet valve 8 does not commence until in the control chamber 16 a certain minimum pressure exists, which is determined by the tension of the counter-spring 24. In the cylinder chamber 4 behind the surface 3 0f the working piston has to exist a certain minimum pressure for the opening of the outlet valve 12 and for the enforcement of a current against the flow-off pressure within the flow-off chamber 13, in order to guarantee the return movement of the piston. This pressure is produced before the offset surface 2 of the working piston by the higher pump pressure in the cylinder chamber 4 (higher in conformity with the ratio of the two piston surfaces 2 to 3). This piston pressure is caused by the spring 24 preventing the pressure oil from flowing, and consequently also the pressure from dropping below this minimum pump pressure.

The working piston follows the control pin c, within the limits dictated by the working capacity of the driving pressure oil pump, with high precision in direction and speed. The forward movement and return movement of the working piston will then constantly repeat themselves through the outer forward feeding of the pilot valve, so that the timing of the forward feeding control means dictates the timing of the working piston. The working piston a follows the forward feeding or the control pin 0, driven during its forward movement and braked during its return movement by the forward feeding control means, with slight variations, resulting from a change of position of the control pin valve head with respect to its seat, caused by the pressureand viscositydepending quantity of control oil. Because of the large valve seat, these variations or inaccuracies are in practical use no longer measurable.

From the foregoing said before it will be apparent that it is not necessary to subject the individual sliding surfaces of the sliding valve to precision shaping, as, even in cases of not perfectly closing surfaces, the oil will constantly glow in the desired direction. Precision shaping is required only at those surfaces which close up the valve chamber 7 against the compartment containing the spring 24, in order to avoid any interference with the effect produced by the spring 24. For the removal of oil drippings and in order to enable the pumping movement going on in this chamber because of the movement of the inlet valve body 9, the valve pin 0 is provided with an axial bore (shown in dotted lines) which opens behind the valve pin head 19 and thus is in communication with the flow-off chamber 13.

' The graphical illustration of Fig. 4, in which P indicates the pressure of the oil supplied by the pump, P the pressure in chamber 13, and Pst the control pressure in the control chamber 16, shows at which rise and fall of the pressure in the control chamber 16 the valve movements commence. The horizontally hatched field, in which at the end of every piston stroke both valves are closed, can be made narrower or wider in any desired way through alteration of the hereinbefore described four annular surfaces acted on by pressure, so that it is possible in this Way to have the valve movements follow one another in quicker or slower succession. The straight line inlet valve opens may approach a line starting in the graphical illustration less than 45 degrees from the zero point, and the straight line outlet valve opens may closely approach the line P in order to obtain the slowest succession of the valve movements. -On the other hand, a narrow field both valves closed may be positioned anywhere between these two outmost angular positions. This shows that not only the aforementioned quick or slow succession of the valve movements is possible, but that also the sensitiveness of the pilot valve can be changed through reaction to lower or higher pressures in the control chamber.

As an example of an actuating means for the pilot valve, there has been described with the aid of the construction shown in Fig. 1 a hydraulic actuating device. For the operation of this valve actuating device, the valve pin 0 has been provided with an extension 27 which extends through the outlet valve. Aligned with extension 27 is the one end of a control pin 28, whose other end forms piston 29 which is guided in a cylinder 30. The movement of the control pin is limited by abutment at the end of the cylinder 3%. The cylinder 30 is via a bore 31 in cylinder b and a conduit 32 in communication with a longitudinal bore 33 of a cylinder body 34 provided with an offset cylindrical extension 35 on which a tubular piston 36 is shiftably supported. The longitudinal bore 33 of the cylinder body 34, 35 opens into a cylindrical chamber 37 whose surrounding walls are formed by the front face of the cylinder 35, the bottom 36a of the tubular piston 36, and the tubular piston 36. These hollow spaces are, as will be described later, deaerated and filled with oil at every working stroke. The tubular piston 36 has its free end run by means of a roller 38 or the like on the circumference of an eccentric disk 39 whose driving shaft 40 can be made to rotate with infinitely variable speed regulation. For every one of the described working units, there is a special eccentric cam 39 mounted on the shaft 49 for regulating the valve actuating means. The outercircumferences of the eccentric cams are given any required shape in conformity with the desired cooperative actuation of the working pistons, so that, for example, a multiple forward and return movement of a working piston during a revolution of the shaft is feasible. In the embodiment of Fig. 1 the simplest form of an eccentric cam is illustrated. The position of the valve actuating means, in the embodiment of Fig. 1, is in conformity with the position of the piston at the end of a stroke. When the shaft 41 with its eccentric disk 39 is rotating, the tubular piston 36 rests with its roller 38 against the eccentric disk until the base circle 41 has been reached. As hereinbefore already described, there is in the chamber 13 of the unit a pressure above atmospheric of, for example, 2.5 atm. This pressure actsupon the front face of the .control pin 28 confronting the pilot valve, as well as upon the annular surface of the control pin piston 29. In the cylinder 34!, the connections 31, 32, 33 and the cylinder chamber 37, which are filled with hydraulic fluid, the same pressure comes into existence, bears against the front face 364: and forces the roll 38 against the eccentric disk 39. Rotation of the shaft 40 results in shifting of the tubular piston 36 and of the control pin piston 29 with the oil column positioned between them, maintained for example at a pressure of 2.5 atm. and surrounded by the cylinder walls and pipe connections, in the direction enforced by the eccentric disk, that is to say, the control pin 28, 29 follows precisely the movement of the tubular piston 36 which is rigidly secured to the roller 33. Which means that, as hereinbefore already described, through rolling of the roller 38 upon the eccentric 39 the accurate succession of the working piston with the hydraulic increase in power is enforced. in order to avoid for the eccentric disks 39 unduly large diameters, it is possible to increase the ratio of the cross-sections of the cylinder chamber 37 to the cylinder chamber 30, so that the ratio is 2:1 or 3:1, in which case already comparatively slight axial movements of the tubular piston 36 result in large axial movements of the control pin piston 29. During the forward and return movement of the preliminary control drive, there come into existence through action of the weak spring 42, through friction and through forces due to the mass, variations in pressure of the oil column. These, however, are without importance because of the small compressibility of the oil. Simultaneously, however, there are oil losses through leakage, which shorten the oil column, while outer fluctuations of temperature likewise cause changes. That is why the height of the eccentric cam 39 has been slightly increased as compared with thedesired path of operation of the piston a, with due consideration of the ratio of transmission resulting from the differently sized cylinder chambers 37 and 30 of the forward feeding control means. During the return movement, the control pin piston 29 is arrested by the cover of the working cylinder b when striking against it, shortly before the roller 38 reaches the base circle 41 of the eccentric disk 39. At this moment the pressure in the forward feeding control drive drops. The return valve 46, which is arranged in the flow-off chamber 13 and kept under a spring tension of, for example, 1 atm., feeds, while reducing the pressure for 1 atm., oil from the flow-off chamber 13 into the connecting pipe 31, so that the roll 38 continues to stay pressed against the eccentric cam 39. When in the end position the roll 38 touches the base circle 41, transverse bores 45 of the cylindrical body 34, 35 and transverse bores 44 of the tubular piston 36 are brought to register, so that the oil from the chamber 13 is enabled to flow through these transverse bores into the cylinder chamber 48 and through the pipe connection 49 into a store vessel for oil, the preliminary control drive is completely filled up with oil and simultaneously de-aerated. When the shaft 40 and the eccentric cam 39 continue rotation, the tubular piston 36 is again displaced in forward direction, the flow of oil through the transverse bores 44 and 45' stops, the

rise of pressure in the preliminary control drives closesimmediately the return valve 46, the oil column filled up to full volume displaces the control pin and effects the forward movement of the piston a. Also in the direction of the forward movement a slight excess of displacement takes place, which can be regulated at will through corresponding alteration of the height of the eccentric cam 39. The tools fastened at the Working pistons a, as shown in the illustration, come to rest against each other in the end position of the working pistons, after the bending work to be done has been completed by them. As in this end position the tubular piston 36 of the preliminary control drive is additionally advanced by the eccentric cam 41 for a small value, the pressure in the preliminary control drive rises up to the splashingofi pressure of a safety valve (not shown in Fig. 1) screwed into the bore 43 of the cylinder body 34. Through repetition at every stroke of this flowing-through, refilling and de-aeration during the return movement, and slight splashing-off at the end of the forward movement, losses through oil leakage are counter-balanced and variations of volume through temperature fluctuations are made ineffective. That is why this hydraulic preliminary control device works with a correctness desirable for the utilization of the pilot valve precision.

The tubular piston 36 is surrounded by a stationary casing 47 in which the tubular piston is guided by means of an outer annular offset portion 36b. The inner space 48 of the casing 47 as well as the pipe branches 49 serving, when the device is in operation, for the discharge of oil flowing in from the flow-off chamber 13, may be connected with the store vessel which via the bore 14 is in communication with the flow-oif chamber 13. That is why, for the exchange of the eccentric cams when the preliminary control drive is arrested, all tubular pistons can simultaneously be moved into the outmost position shown in Fig. 1, as the pressure of the store vessel acts upon the annular oiIset portion 36b of the tubular piston 36 and displaces the tubular piston. actuation of the preliminary control means does not also cause a forward movement of the working piston, the pressure of the driving pump is regulated down to the minimum pump pressure determined by the spring 24. In this way an opening of the inlet valve, and accordingly also a forward movement of the working piston, is made impossible. The oil displaced in the preliminary control means is, as hereinbefore already described, splashed oh. by the safety valve screwed into the chamber 13.

While in the embodiment of Fig. 1, the housing for the valve arrangement is-forced by piston a the valve of the embodiment of Figs. 2 and 3 is provided with a housing positioned between an oil pressure pump provided with output regulatorand output limitation and the cylinder of a working piston. In the embodiment of Figs. 2 and 3, the parts of the pilot valve corresponding to those of the embodiment of Fig. l have-been denoted by the same reference numerals.

In the embodiment of Figs. 2 and 3, there have been employed two pilot valves A and B of the same type corresponding to the pilot valve of Fig. 1. The casings of the pilot valves 51 and 51a are fastened, in sealed condition, in the walls of an oil tank 52 in such manner that the inlet valve ends are located outside the oil tank, and that the outlet valve ends open via bores 53 and 53a in the casings 51 and 51a into the tank 52. The oil level in the tank 52 is located at such height that the outlet openings 53 and 53a are positioned below the oil level.

Here again, the pilot valve consists of an inlet valve body 9 providedwith valve head 8, an outlet valve 12, and a control pin or control slide, which in this case is of modified construction as compared with the construction of Fig. 1. The outlet valve 12 is again of the tubular cylindrical type, whose outer front face forms the valve head, and whose inner front face forms the one side of the control chamber 16. This control chamber 16 consists of an annular cylindrical recess in the inlet valve body 5, which is open only in the direction toward the outlet valve and into which the outlet valve 12 is accurately fitted. With the aid of the aforesaid construction of the pilot valve, guided only at one end by means of against a flow-olf chamber formed in this case by the oil tank 52, or opens the connection. The oil conduit 54 In order that this.

extending from the oil pump 54} and in which a return valve 55 is arranged, leads to the inlet valve chambers 7 of both of the pilot valves. The outlet valve chamber 11 of the lower pilot valve A is connected via the conduit 56 with the working cylinder at the upper end of the cylinder 57, while the outlet valve chamber 11 of the upper pilot valve B is connected via the conduit 86 with the intermediate rapid motion cylinder chamber 570. In addition to this, the oil pressure pump is connected via a branch pipe 59 with the lower end of the cylinder 57a. The piston operating in the cylinder parts 57 and 57a is a differential piston 58, 58a, whose mode of operation in cooperation with the pilot valve will be described later.

There works in the inlet valve body 9, in an axially stepped longitudinal bore a control pin or control slide. This control slide consists of three pistons 61, 62 and 63 sealing within the bore, and which by means of connee-ting rods 64 and 65 (see Fig. 3) are jointly displaceable within the inlet valve body. The intermediate piston 62 is provided with an obliquely extending bore 66 (indicated in broken lines) which in the middle of the piston is of smaller diameter and in this way enables a throttled flow of oil between the annular spaces surrounding the rods 64 and 65. The annular space 67 is connected by means of one or a plurality of radial bores 68 with the inlet valve chamber 7, while the annular space 69 is connected via radial bores 70 with the control chamber 16. In addition to this, it is possible to put the annular chamber 68 into connection via a radial bore 71 and a longitudinal bore 72 with the flow-off chamber 52 when the piston 63 uncovers the radial bore '71, as will hereafter be described.

The control slide projects with an extension from the casing 51 and is at its free end devised as armature 73. It extends'through two magnet coils 74 and 75 which through alternate connection with a source of voltage displace the armature 73 and consequently also the control slide in either one direction or the other. Both of the magnet coils are arranged in a casing 76 (see Fig. 3) which (for reasons to be explained later) is secured to the end of the sealing piston 9 which freely projects from the cover of the casing 51. When the magnet coils 74 and 75 are de-energized, the armature 73 and the control slide connected to it take up a zero position, in which the control slide piston 63 partly covers up the radial bore 71. The control oil flows from the inlet valve chamber 7, which is constantly under pump pressure, via the radial bore 68 into the annular chamber 67, from there through the throttle bore 66, which takes care of a limita- I tion of the quantity of control oil to a required volume,

to the annular chamber 69, and into the control chamber 16. From this chamber the oil flows through the bores 71.and 72 into the flow-off chamber or tank 52. The control slide piston 61, facing the double magnet, has a slightly larger diameter than the intermediate control slide piston 62. This difference in size of the pressure surfaces causes, as both of the front faces of the pistons are acted on by the pump pressure, a force acting in the direction of the magnet. However, the diameter of the control slide piston 63 is slightly larger than even the diameter of the piston 61. That is why the pressure existing in the annular chamber69 and consequently also in the control chamber 16 produces, because of this second and larger difference in the size of the pressure surfaces, an oppositely directed force. The control slide automatically adjusts itself in such a position that the return fiow of the control oil via the forward control edge of the slide piston 63 and the bore 71 corresponds to the control oil flow through the throttle bore 66 and that in the control chamber 16 a pressure exists which is in fixed proportion, determined by the difference of the pressure surfaces, to the pump pressure. In zero position of the control slide, this control pressure keeps the outlet valve closed, but does not suffice to open the inlet valve. When applied to the graphical illustration of Fig. 4, this control pressure would, in the zero position of the control slide in its linear dependence upon the pump pressure P be illustrated in a straight line positioned in the horizontally hatched field both valves closed.

The pump pressure closes the inlet valve through its action upon the annular surface determined by the diameter of the inlet valve seat and the diameter of the inlet valve body 9 guided in the cover of the casing. The spring 24 assists in this closing and prevents, for a reason to be explained later, the opening of the inlet valve 8, 9 from occurring before a minimum pump pressure has been reached. The front end of the annular cylindrical recess of the inlet valve body 9 which faces the inlet valve and in the rear end of which the outlet valve is guided, is acted on by the control pressure in the control chamber 16 for the opening of the inlet valve. The control pressure acts upon the same annular surface determined by the inner and outer diameter of the outlet valve for the closing of the outlet valve. The pressure coming into existence during the return movement of the differential piston 58, 58a at the upper piston surfaces through action of the pump pressure upon the lower annular return movement surface, which via the conduits 56 and 80 effects the outlet valve chambers 11, acts upon the annular surface determined by the valve seat diameter and said outer diameter of the outlet valve and opens the outlet valve. In order to keep the dimensions of the outlet valve as small as possible, this opening force is aided by the spring 25. These four surfaces acted on by the pressure are in suitable manner differentiated with respect to one another, as described already for the form of construction of Fig. 1. The possibilities described already with the aid of the graphical illustration of Fig. 4 apply without restriction also to the embodiment shown in Figs. 2 and 3.

Proceeding now from the de-energized zero-position of the two pilot valves, we find the piston 58, 58a at rest. The pump pressure acts via the conduit 59 and the lower cylinder chamber 57b upon the annular surface 6i) of the differential piston 58a. In the working cylinder chamber 57 and in the rapid action cylinder chamber 570 is thereby produced a counter pressure, which via the conduits 56 and 80 effects the outlet valve chambers ll. In the self-controlled zero-position of the control slides, with magnets de-energized, the closing force of the outlet valves predominates. When, now, the two coils 75 and 75a are energized, the control slides are displaced toward the right. The control oil can flow off from the control chamber 16 via the bores 71 and 72. Both of the outlet valves open because of the aforedescribed counter oil pressure and the effect produced by the springs 25. The piston 53, 58a is displaced in upward direction. As for the filling of the small cylindrical annular chamber 57b the full pump effect is at disposal, this return movement of the piston takes place with great speed. In the desired end position the coil 75a is de-energized, the control slide of the pilot valve B moves immediately into zero position, the control pressure rising in this pilot valve in the control chamber 16 closes the outlet valve. As the return flow from the cylinder chamber 570 is interrupted, a rise of pressure takes place in this chamber which counterbalances the pressure in the cylinder chamber 57b, so that the piston terminates its return stroke. The coil 75 of the control slide in the pilot valve A remains energized, so that this outlet valve stays open. When, now, the coil 74a is energized, the control slide in the pilot valve B is displaced to full return flow throttling of the control oil. The pressure in the control chamber of the upper pilot valve rises to the pump pressure, the outlet valve is pressed against its seat, and the inlet valve opens. The pressure oil conveyed by the pump does now flow through the conduit 54-, inlet valve chambers 7, connecting branch 77 (see Fig. 2) or connecting channel 78 (see Fig. 3) via the upper inlet valve through the upper outlet valve chamber 11 into the conduit 8t) and fills the rapid action cylinder chamber 57c. As the annular piston surface 81 acted on in this chamber is larger than the return pressure surf-ace 69, the piston 58a is pressed in downward direction and the pressure oil located beneath the piston in the cylinder chamber 57b is displaced through the conduit 59 via the aforedescribed path. As the cylinder chamber 570 is comparatively small, the full pumping effect moves the piston down in rapid motion action. This movement results in the cylinder chamber 57, above the large piston 58, in a partial vacuum, which sucks up from the oil tank 52 via the lower outlet valve (which is still open), the outlet valve chamber 11 and the conduit 56, oil for the preparatory filling of the working cylinder. Shortly before the tools hits the workpiece, the magnet coil 75 is disconnected and the magnet coil 74 connected, the control slide of the pilot valve A effects through its forward shifting an immediate rise in pressure in the control chamber 16. As a result of this, the outlet valve in the pilot valve is closed and the inlet valve opened. Now, the pressure oil of the pump is supplied to both of the upper cylinder chambers via both of the inlet valves and via the conduits 8t) and 56. The complete upper piston surface, composed of the surface of the working piston 58 and the annular surface of the rapid action piston 81, is acted on by the pressure oil. The piston moves in slow working motion additionally forward for the deformation of the workpiece. The working effect of the piston, in its dependence upon path, pressure or time, is interrupted through disconnection of the two coils 74 and 7 :51. There is caused an exitation of the two magnet coils 75 and 75a, whereupon with the return movement of the piston, the described cooperation of electrical forward feeding control means, pilot valves, and pistons repeats itself.

The mode of operation of this preliminary control means (in the embodiment: an electrical forward feed ing) is indicated in Fig. 2 by the broken lines 8;, S and S When the two coils connected with each other by the line S are energized, the forward movement of the piston takes place in rapid action motion. When the two coils connected by the line S are energized, the for ward movement of the piston is changed to slow working action. Exitation of the two coils indicated by the line S results in acceleration of the return movement of the piston.

The weight of the piston, inclusive of upper tool, which is secured to the freely extending plunger of the piston, has to be counterbalanced by a constantly effective minimum pump pressure. Furthermore, the pump pressure has to be so proportioned that during the return movement of the piston a return flow from the upper cylinder chamber is enforced. This minimum pump pressure is guaranteed by the springs 24 permitting only at a certain minimum pressure an opening of the inlet valves.

The opening of the inlet valve 8 is limited through the stop offered to the valve head by the edge 7s. The magnet casing 76 containing the two magnet coils '74 and 75 or 74a and 75a, respectively, is fastened on the portion of the inlet valve body 9 projecting through the cover of the casing 51 and moves with the inlet valve 8, 9. The armature 73, with the control slide 61, 62, 63 rigidly connected to it, therefore, has to perform only the small movements necessary for the complete covering up and for the complete uncovering of the outlet bore '71 for the control oil. In the embodiment shown in Fig. 3 this stroke of the armature from the intermediate position is only 3 mm. in every direction. This control means, therefore, works practically without inertia with very small outer forward feeding control forces, in this embodiment: electrical forward feeding forces.

In order to relieve the pump, which as regulating pump follows every'operating action through immediate subsequent regulation of the quantity to be conveyed, and in 11 order to enable a smooth working of the entire hydraulic, a store vessel 82 may be connected with the oil pressure conduit 54.

In order to achieve after every reciprocating cycle of the diflerential piston a de-aeration of the cylinder chambers 57, 57b and 570, there are connected to these cylinder chambers 57 and 570 two throttle conduits 83, which via helically wound flow resistance tubes 84 are led back into the oil tank 85, from which the pump 50 takes its operating oil. The lower cylinder chamber 57b is corr nected via a throttle bore 86 (indicated in broken lines) and a flow resistance tube, arranged in the bore 87 of the differential piston, with the cylinder chamber 57, so that a constant de-aeration of the cylinder chambers takes place.

From the described forms of construction for the utilization of the pilot valve of the invention it will be seen that in each case large sections of flow are obtainable in the valves, and that because of the small movements, the valves work practically without inertia. Apart from this, the performance or power necessary for the preliminary control, which may be of the electrical, hydraulical or mechanical kind, is a very small one, and the control mechanism may be devised with very small dimensions, whereby it will work without loss of time. As the pilot valve works practically without inertia, numbers of strokes can be obtained which have hitherto been completely impossible for oil pressure presses or other machines operating with reciprocating working pistons. Furthermore, practical tests have taught that, when working units like the one illustrated in Fig. l are employed, no heating of the pressure oil will occur also through continuous working, which shows that the laminar flow can without difiiculty be obtained with small oil speeds.

The pilot valve of the invention can be employed also for a sensitive control in which the valves are opened and closed in infinitely variable manner. In the latter case, the pilot valve is provided with two control chambers. The inlet and outlet valves are then loaded with hard springs of the desired characteristic, whereby the preliminary tension of the springs may be affected by the entering pressure. The preliminary control is thereby eflected by means of a longitudinal slide, which changes for both valves in stepless variable manner the ratio of entering pressure to control pressure.

Furthermore, through rigid or adjustable limitation of the valve openings, every desired throttling of the oil flow in the valves can be effected. As the throttling takes place at the sharp-edged annular surface of the valve seat, the eflect produced by the viscosity of the oil upon the flowing quantity is considerably reduced.

in addition to the embodiments described in the specification, there are also other possibilities olf application quite feasible.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A valve for the controlled feeding of hydraulic fluid comprising a valved inlet, a valved outlet, a control chamber formed in said valve, said chamber being in communication with the valved inlet and outlet, a relatively restricted passageway formed in said valve for the passage of hydraulic fluid to the control chamber for the building up of pressure in the control chamber suflicient for closing the valved outlet and opening the valved inlet, a control valve for releasing fluid from the control chamber when a predetermined pressure is reached therein thereby effecting the opening of the valved outlet and the closure of the valved inlet, and means for closing the control valve after the inlet valve has been closed as aforesaid.

2. The valve according to claim 1 wherein the means for closing the control valve is hydraulically powered.

3. The valve according to claim 1 wherein the means for closing the control valve is electrically powered.

4. A valve for the controlled feeding of hydraulic fluid comprising valved inlet means, valved outlet means, a control chamber formed in said valve intermediate sa1d inlet and outlet means, said chamber being in communication with said inlet and outlet means, a restricted passageway formed in said valve for the passage of limited quantities of hydraulic fluid to the control chamber for the gradual building up of pressure in the control chamber sufficient to first close the valved outlet and then open the valved inlet, a control valve for releasing fluid from the control chamber when a predetermined pressure is reached therein thereby effecting the opening of the valved outlet and the closure of the valved inlet, and means for closing the control valve after the inlet valve has been closed as aforesaid.

5. A valve for the controlled feeding of hydraulic fluid comprising valved inlet means, valved outlet means, a control chamber formed in said valve, said chamber being in communication with said inlet and outlet means, a restricted passageway formed in said valve for passing limited quantities of hydraulic fluid to the control chamber for the gradual building up of pressure in the control chamber sufficient to first close the valved outlet and then open the valved inlet, the hydraulic fluid flowing into the valve through the valved inlet passing into a second chamber formed in said valve, a control valve for releasing fluid from the control chamber when a predetermined pressure is reached therein thereby elfecting the opening of the valved outlet and the closure of the valved inlet, the hydraulic fluid being released from said second chamber with the opening of the valved outlet, and means for closing the control valve after the inlet valve has been closed as aforesaid.

6. The valve according to claim 5 wherein the valved inlet means, the valved outlet means and the control valve are spring biased.

7. A control valve device for servo-mechanisms with a dilferential piston loaded only on one side, comprising an inlet valve, an outlet valve, a housing common to said inlet and outlet valves, said inlet and outlet valves arranged to open and to close in the same direction, means within said housing to define a control chamber intermediate said inlet and outlet valves, means to continuously feed said control chamber with a predetermined quantity of throttled fluid, and an auxiliary means to control the positions of said inlet and outlet valves.

8. A control valve device in accordance with claim 7, wherein the power for the opening and the closing of said inlet and outlet valves is supplied by the impingement on four annular surfaces of said valves by pressures acting in the servo-mechanism and the valve housing including: the annular surface formed by the valve seat diameter of said inlet valve and the outside diameter of a rod supporting said inlet valve which is acted on by the pressure for closing said inlet valve; the annular surface on the face of said inlet valve which is acted on by the pressure for opening said inlet valve; the annular surface of said outlet valve which is guided in said control chamber by the pressure for closing said outlet valve; and the annular surface formed by the valve seat diameter and outer diameter of said outlet valve which is acted on by the pressure of the fluid for opening said outlet valve.

9. A control valve device as set forth in claim 7, wherein a spring is positioned to act against said inlet valve so that said inlet valve is opened only when the pressure in said control chamber is reduced to a predetermined minimum value.

References Cited in the file of this patent UNITED STATES PATENTS 477,055 Kieckhefer June 14, 1892 597,388 Brown Jan. 18, 1898 929,206 Gelpke July 27, 1909 2,639,693 Miller May 26, 1953 

